1. Field of the Invention
The present invention relates to triazineone compounds for treating animals infected with parasites that cause abortigenic or neurologic diseases. More specifically, the present invention relates the triazineone compounds that are useful in treating parasitic protozoa such as coccidia that cause abortigenic or neurologic diseases.
2. Brief Description of the Prior Art
Triazineone compounds such as triazinediones, e.g., diclazuril compounds, and triazinetriones, e.g., toltrazuril compounds have been used in treating and protecting various mammals, insects and fish from diseases caused by a broad range of protozoa. See U.S. Pat. Nos.; 4,933,341; 4,935,423; 5,114,938; 5,141,938; 5,188,832, 5,196,562, 5,256,631 and 5,464,837. Protozoa sensitive to these compounds include parasites, which infect the intestines of birds, mammals and insects and manifest as diarrhea, wasting, nausea and vomiting. Generally, the mode of action of the triazineones is to attack the intermediate parasite stages found in the gut and intestinal wall cells, causing the endoplasmic reticulum, the perinuclear space and the mitochondria of the parasite to swell. This purportedly disturbs the ability for nuclear divisions causing the shizonts and microgamonts to remain small forming only a few merozoites and microgametes respectively. The end result is reported to be the loss of the ability of these latter stages of the parasites to penetrate new mammalian cells, effectively halting the replication of the parasite in the host.
Of particular concern here are certain protozoa suspected of causing neurologic and/or abortigenic diseases of animals since the 1970's. Successful isolation and in vitro cultivation of some of these protozoa proved to be difficult. For example successful isolation from the brain or cerebral spinal fluid were not accomplished until the late 1980s. Once it was determined that neurologic diseases could be produced by parasites infecting the brain and abortigenic diseases could be produced infecting the fetus, there was a need for effective anti-protozoa drugs which could cross the blood-brain barrier and the placental barrier without producing deleterious side effects. Very few drugs are able to pass the blood-brain barrier or the placental barrier of animals. However, many of the art-known drugs that can to cross the blood-brain barrier and/or the placental barrier to effectively treat parasitic infections of the brain have detrimental side effects such that they cannot be used without great risk. Therefore, there have been no effective drugs approved to date which provide an effective treatment for such neurologic or abortigenic diseases. The following is a brief description of the parasitic diseases.
Equine Protozal Myeloencephalitis (EPM) is a neurologic disease of horses, with a predilection for young horses undergoing stress (e.g., thoroughbred race horses and purebred performance horses), and is thus a disease with significant monetary impact for the horse industry. EPM, first recognized as a disease in the 1970's, was not cultured from a horse with EPM and given the name Sarcocystis neurona until 1991. In 1997, a Neospora spp., now named Neospora hugesi, was isolated from the brain of a horse with EPM. Accordingly, it is now proposed that EPM may be caused by this newly recognized organism alone, by Sarcocystis neurona alone or the combination of the two. EPM most often results in asymmetric incoordination (ataxia), weakness, and spasticity. The disease can mimic almost any neurologic condition. It can occur as a peracute or chronic condition. The chronic form is often insidious at onset, difficult to diagnose until late in the course of the disease, and can result in death. In the mildest cases, the only clinical sign may be ill-defined pelvic limb lameness or a minor respiratory noise. In the most severe cases, horses are unable to swallow or stand. It is now known that in the most severe cases, the parasite, e.g., S. neurona infects the brain and produces significant damage therein. The clinical signs of EPM are caused by direct neuronal (brain and spinal cord) damage by the parasites as well as brain damage resulting from infiltration of inflammatory cells, edema, and neuronal death associated with merozoites and meronts in the central nervous system (CNS). Currently, there is no approved effective treatment or prophylaxis for the control of EPM. The human drug trimethoprim-sulfonamide combination has been used. However, treatment is expensive and requires an extensive number of repeated doses.
Another coccidian parasite, Toxoplasma gondii, has been known for some time and was first isolated from the intestines and muscle tissue of cats. The definitive host for this parasite is the cat that can harbor the organism for long periods of time spreading oocysts to other animals including bovines, ovines swine and humans. Infection of sheep, cattle and humans has been associated with abortion and congenitally acquired disorders, which primarily affect the central nervous system. It has also recently been associated with abortion and malformation in kittens born to infected queens that had been seronegative prior to infection during pregnancy. Non-feline hosts such as bovines, ovines swine and humans do not produce oocysts but develop and may suffer from invasion of muscle and brain by tachyzoites and bradyzoites which produce the clinical signs of disease--neurological symptoms and abortion with fetal defects. It has been reported that 60% of cats are serologically positive to T. gondii. Once again, there is no approved treatment or prophylactic for toxoplasmosis.
Yet another coccidia parasite, Neospora caninum, produces both a neurologic and abortigenic disease in animals. It was first isolated from dogs in 1988. It was previously confused with Toxoplasma gondii. The disease caused by this parasite occurs most severely in transplacentally infected puppies and is characterized by progressive ascending paralysis in the puppies, particularly of the hind limbs; polymyositis and hepatitis may also occur. This disease has more recently been recognized as a major cause of abortion and neurologically-associated limb defects in newborn calves. Microscopic lesions of non-suppurative encephalitis and myocarditis in aborted fetuses may be seen in the brain, spinal cord and heart. A definitive host for Neospora caninum has recently been identified to be the dog. At this time there is no approved treatment or prophylaxis for either Neospora caninum of dogs or bovines or Neospora hugesi of horses.
Art-known references, including the above-cited references do not suggest or teach the use of triazineone compounds such as Toltrazuril or Toltrazuril Sulfone (recently renamed "Ponazuril") in treating animals infected with coccidia or, more specifically, of the family Sarcocystidae causing abortigenic or neurologic diseases without causing intolerable side effects. There is, therefore, a need for an improved and safe treatment for animals afflicted with parasitic diseases manifesting as neurologic or abortigenic diseases.